The present invention relates to particulate loose-fill insulation. More particularly, it relates to an improved particulate thermal insulation formed of expanded perlite having a slightly tacky coating thereon.
The product of the present invention is formed from expanded perlite ore. Perlite ore is a naturally occurring volcanic mineral consisting primarily of silica, alumina and a small amount of water. Exposure of perlite ore to temperatures in the range of 1700.degree. to 2100.degree. F. softens the mineral and causes the water to expand to form a light cellular mineral particle. Due to the low density and low thermal conductivity of expanded perlite, it has found utility as a thermal insulator. Expanded perlite has been incorporated with other insulating materials to form board-like products and it has also been used in its particulate form as loose-fill insulation. The present invention is primarily concerned with the improvement of the properties of particulate expanded perlite when it is used as loose-fill insulation.
One of the major drawbacks to using particulate expanded perlite in such applications is that its bulk density, and hence its thermal conductivity, increases as the particles settle after their initial placement around the article to be insulated.
Particles of expanded perlite have densities of approximately 2 to 10 pounds per cubic foot. When particulate expanded perlite is initially poured into a container, for example, it has a bulk density of approximately 4 pounds per cubic foot. The individual particles, however, have a tendency to settle, which densifies the mass and significantly degrades the effectiveness of the thermal insulation. The fraility of the individual perlite particles also contributes to this problem. Fracture of individual particles causes settling, and the filling of air space among particles with perlite fragments of higher density than the larger unfragmented particles.
U.S. Pat. No. 2,625,512 to Powell attempts to eliminate such a problem by adhering the perlite particles and fragments together into agglomerates by the use of adhesives. The adhesive is applied as a discontinuous film or as droplets on the expanded perlite particles and fragments at high temperatures. The particles and fragments are then impinged to one another while cooling to promote agglomeration into larger particles. At room temperature these larger particles (or agglomerates) are non-tacky and will "flow" as a granular solid for use as loose-fill insulation. This agglomeration is taught to reduce the tendency of the particulate insulation to densify in relation to its initial bulk density by settling to a higher density.
By contrast, the present invention coats expanded perlite particles with a material that renders the particles slightly tacky at room temperature. The particles can still be treated as loose-fill insulation, in that they can flow and conform to whatever containment is given the particles. The slight tackiness, however, prevents the particles from sliding over one another to pack or densify after initial placement. This increases the thermal efficiency of this type of insulation by preventing the degradation of its thermal conductivity by densification due to settling.
Not only does the insulation of the present invention resist settling and densification, but the initial volume of the expanded perlite of the present invention is significantly higher (in some cases up to 100%) than the volume of an identical amount of untreated expanded perlite. In other words, when the loose-fill insulation of the present invention flows into place, the tackiness of the individual particles causes the particles to form a mass having a significantly lower initial bulk density than would be formed from non-tacky particles.
This lower initial bulk density has two major advantages. First, the thermal conductance of the present invention is significantly lower than conventional loose-fill perlite insulation. Second, less perlite is needed to fill a given volume. The lower initial bulk density of the present invention also results in significant cost savings since less expanded perlite is needed to fill the same volume of space to be insulated.
By providing a loose-fill thermal insulation that is initially more thermally effective, the requires less expanded perlite and that is also more resistant to degradation of its thermal efficiency due to settling, the present invention provides a major improvement in expanded perlite loose-fill insulation.
Other advantages of the present invention will be obvious to those skilled in the art, or may be obvious from the detailed description of the invention, or may be apparent from practice of the invention.